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1.
Science-based management of shallow-water habitats is limited by information on the spatial distribution of properties of sediments. This limitation in part stems from the lack of an adequate model or system to classify and delineate subaqueous soil types (sediments). Present classification systems are inadequate because the existing paradigm does not actually consider them as “soils” but merely as “sediments”. Field observations suggest that these sediments could be better understood as “soils”, and the present paradigm could be modified to incorporate a new one—a pedological paradigm. We propose the application of a pedological paradigm for subqueous soils of subtidal habitats to develop ecological interpretations of subaqueous soil types and apply an inventory of subaqueous soil resources for management of estuarine shallow-water habitats. *** DIRECT SUPPORT *** A01BY074 00009  相似文献   

2.
This study reports the first ethanol and acetaldehyde measurements in sediment porewaters collected at multiple freshwater locations. Ethanol concentrations ranged from 11 to 2535 nM and acetaldehyde concentrations ranged from 6 to 320 nM. A significant positive correlation (p < 0.001) was observed between ethanol concentrations and the percent organic carbon content of sediments (TOC). Porewater depth profiles at two sites within the same lake indicated potential diffusion of ethanol into sediments from the overlying water at a lower TOC site and upwards diffusion from sediment into the water column at a higher TOC site. Diffusion of water column ethanol into sediments was observed at individual sites from October to January, whereas the opposite was true from June to August indicating the seasonal variability of ethanol flux from sediments. Changes in ethanol concentrations during a long-term sediment incubation experiment showed an inverse relation with acetaldehyde concentrations. The lack of a quantitative conversion was likely due to other sources and sinks that control their abundance. Our study provided new information on the biogeochemistry of ethanol in freshwater sediments and shed light on the potential role of ethanol in the global carbon cycle.  相似文献   

3.

Four meadows of turtle grass (Thalassia testudinum Banks ex Konig) in Sarasota Bay, Florida were sampled on a bimonthly basis from June 1992 to July 1993 to determine spatial and temporal variation in short shoot density, biomass, productivity, and epiphyte loads. Concurrent with the seagrass sampling, quarterly water-quality monitoring was undertaken at ≥3 sites in the vicinity of each studied seagrass meadow. Three months after termination of the seagrass sampling effort, a biweekly water-quality monitoring program was instituted at two of the seagrass sampling sites. In addition, a nitrogen loading model was calibrated for the various watersheds influencing the seagrass meadows. Substantial spatial and temporal differences in turtle grass parameters but smaller spatial variation in water quality parameters are indicated by data from both the concurrent quarterly monitoring program and the biweekly monitoring program instituted after termination of the seagrass study. Turtle grass biomass and productivity were negatively correlated with watershed nitrogen loads, while water quality parameters did not clearly reflect differences in watershed nutrient inputs. We suggest that traditional water-quality monitoring programs can fail to detect the onset or continuance of nutrient-induced declines in seagrass health. Consequently, seagrass meadows should be monitored directly as a part of any effort to determine status and/or trends in the health of estuarine environments. *** DIRECT SUPPORT *** A01BY074 00029

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4.
Seasonal patterns of microbially-mediated nitrogen cycling via the nitrification-denitrification pathway were compared between a natural and a restored salt marsh. Sedimentary denitrification rates, measured with a modification of the acetylene block technique, were approximately 44 times greater in the natural marsh relative to an adjacent transplanted marsh. Nitrification rates were similar at both sites. The difference in denitrification rates was attributed to oxygen inhibition at low tide and tidal flushing of porewater nutrients at high tide in the coarse sediments of the restored marsh. Denitrification was positively correlated with nitrification throughout the year in the natural marsh with a seasonal fall peak in denitrification corresponding to a maximum in porewater ammonia concentration. A weak correlation existed between the two processes in the restored marsh, where nitrification rates exceeded denitrification rates by a factor of 20. Transplanted marsh denitrification rates exhibited a spring peak, corresponding to elevated porewater ammonia concentrations. Our findings demonstrate functional differences in microbial nitrogen dynamics of a young (0–3 yr) restored marsh relative to a mature (>50 yr) salt-marsh system. *** DIRECT SUPPORT *** A01BY070 00008  相似文献   

5.
This study addresses the distribution of total phosphorus (TP) and its inorganic (IP) and organic (OP) fractions, grain-size and organic matter of surface and recent sediments, coupled to the behavior of total and dissolved inorganic phosphorus (TP and DIP) of the water column, of the semi-pristine Guaratuba Bay estuary, SE Brazil. Surface sediment samples were taken at 43 sites spread along the estuarine gradient and recent sediments from 3 short (35 cm long) cores from the upper, central and lower portions of the estuary, respectively. Highest TP and IP concentrations of surface sediments were detected within the upper sector and the transition zone between the upper and central sectors, all characterized by fine sediments, low salinities and water depths. In contrast, the lower sector and its narrow and deep tidal channel, subject to more intense tidal forcing, exhibited a higher fraction of sandy sediments with lower TP, IP and OP contents. In spite of the spatial variability in sediment grain size, IP corresponded to the major fraction of TP in all estuarine sectors and both TP and IP correlated significantly with the fine sedimentary (silt + clay) grain-size fraction. The fine surface sediments acted as a trap for IP at the fresh water–low salinity interface, which also corresponded to the region of a DIP sink in surface waters. In general, the short sediment cores showed that TP and IP contents increased from 15 cm depths to the top layer. Published sedimentation rates from additional cores taken at the sites of the short cores of this study, implied that depositional alterations of TP and IP increased during the early 1970s, which corresponded to the onset of anthropogenic disturbances from crop plantations in the lowland plains of the river end-member and urbanization at the estuary’s mouth and along the adjacent coast.  相似文献   

6.
Polychlorinated dibenzo-para-dioxins (PCDDs) and dibenzofurans (PCDFs) were measured in the tissues of the estuarine clamRangia cuneata at four sites in the Neches River that had been subjected to paper mill effluent and at two remote sites. One of the river samplings was taken before dioxin control measures and another 2 yr after the control measures began. Measurable concentrations of PCDD/Fs were present at all sites, but higher concentrations were present at the Neches River sites. Whole tissue concentrations of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) and all PCDD congeners for the two collections were not significantly different (p>0.05), but lipid-normalized concentrations for the two collections were significantly different (p<0.05). Highest concentrations of PCDDs at sites located 8 km and 16 km upriver from the paper mill effluent outfall indicated that the materials were transported upriver by saltwater intrusion and/or that nonpoint sources existed upriver. The presences of PCDD/Fs in clam tissues from the remote sites also indicated that other sources of these materials existed. Even under extreme physiological conditions (spent reproductive phase, low lipid contents, water temperature 10°C; ripe reproductive phase, high lipids, water temperature 32°C)Rangia cuneata was an effective biomonitor to determine the distribution of PCDD/Fs at specific sites. *** DIRECT SUPPORT *** A01BY069 00021  相似文献   

7.
This paper reports on the aquatic chemistry of trace elements in terms of spatial and temporal distribution, but also pollution sources in the transboundary watershed of the Seversky Donets River (Ukraine/Russia). Bed sediments and filtered water were collected from the Udy and Lopan Rivers at sites from the river source in the Belgorod region (Russia) to rural and urban areas in the Kharkiv region (Ukraine) in May and August 2009. Priority trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn), an urban tracer (Ag) and additional metals (Co, Mo, V) and Th were measured in stream water and sediments. The low levels and variability of Th-normalized concentrations indicated the absence of geochemical anomalies in the upstream part of the rivers and suggested that these data represent a regional baseline for trace elements in bed sediments. In contrast, water and sediments within the city of Kharkiv were contaminated by Ag, Pb, Cd, Cu, Cr and Zn, which are mainly attributed to municipal wastewater inputs and urban run-off. Results of the environmental quality assessment showed that element concentrations in the sediments can be considered as potentially toxic to aquatic organisms in sites downstream of the wastewater discharges.  相似文献   

8.
Benthic fluxes of C, N, P and Si have been measured at two sites in Great Bay Estuary, New Hampshire. Higher fluxes of reactive phosphate, nitrate and reactive silicate were observed at the site where bioturbation is known to occur and the fluxes of NH4 +, PO4 ?3 and reactive silicate at this location were from 3 to 6 times higher than that calculated by simple pore water diffusion models. *** DIRECT SUPPORT *** A01BY019 00010  相似文献   

9.
Salinity can be used as a conservative tracer of porewater turnover in circumstances when evapotranspiration is great enough to concentrate porewater salts in intertidal sediments. At two intertidal sites situated at mean high tide at North Inlet, South Carolina, porewater drainage was estimated by this method to be 9.4 m?2 d?1 and 16.6 1 m?2 d?1, depending on physical soil properties and assuming that solute losses occur by simple diffusion across the sediment surface, by uptake and excretion by vegetation, and by drainage. Mass balance simulations indicated that sediment physical properties, evapotranspiration, and elevation are important determinants of seasonal salinity extremes. At sites situated mear mean high tide, small differences in elevation significantly affect salinity and drainage rate. As site elevation increases, losses of solutes by drainage and diffusion decrease, and the variability of porewater salinity increases. This is significant because interannual changes in mean sea level, which average ±2.9 cm on the South Carolina coast, can have a great impact on the structure and function of estuaries due to changes in the solute balance of intertidal zone sediments. Mass balance simulations that used reduced evapotranspiration rates typical of colder climates significantly reduced the mean and variability of porewater salinity, which suggests that at lower latitudes salinity becomes a more dominant determinant of biological processes. This should influence a number of processes including primary productivity, strategies of water conservation and osmoregulation, and community structure. This conclusion is consistent with published data that show tropical mangroves to have lower photosynthetic rates, and presumably lower gas exchange rates in general, than mid- and high-latitude salt marsh grasses.  相似文献   

10.

Karst aquifers in subtropical regions are characterized by high variability of water availability and quality due to changes associated with rainy and dry seasons. An additional challenge for water management is the combination of surface-water and karst groundwater systems since high spatiotemporal dynamics cause high variability of water quality. In these cases, adapted protection strategies are required. In this study, a protection approach for the catchment of a river-water diversion point in a rural area in northern Vietnam is developed. The variability of water quality was evaluated by rainy and dry season synoptic surveys of suspended particles and microbial contamination at 49 sites and time series at three sets of paired sites under constant hydraulic conditions. The anthropogenic land-use activities in the catchment were mapped to identify potential contamination sources and to highlight the challenging combination of surface-water and karst groundwater management. The analyzed data indicate differences in water quality between the dry and rainy seasons and a higher influence on water quality from land use than from hydrologic conditions. Furthermore, the results suggest a high risk of contamination resulting from residential areas, agriculture, and livestock farming, and reveal the necessity of implementation of appropriate measures such as restricted farming and the hook-up of buildings to municipal sewage disposal. Finally, the data show that water quality can be improved by adjusting water withdrawals by the time of day. The applied methods can be transferred to other surface-water and karst groundwater systems in similar subtropical environments.

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11.
Underground developments such as subways and shopping facilities have been increasing in number and magnitude in the relatively shallow subsurface of many urban areas where the earth materials commonly are composed of marine sediments. Marine sediments can contain significant amounts of toxic trace elements such as arsenic, boron, and lead. Changes in the subsurface environment caused by excavation and construction in underground developments could potentially cause these toxic elements to be dissolved into pore water of the sediments, which might lead to groundwater pollution. The purpose of this study is to investigate correlations among chemical properties of marine sediments, such as pH and electrical conductivity (EC), concentrations of toxic trace elements, and stratigraphic characteristics of the sediments. We selected three sites with different stratigraphic settings in the southern Kanto Plain around the Tokyo Metropolis. We collected core samples from shallow strata at a site in the Arakawa Lowland, southern Saitama, and at two sites in the Musashino Upland, Middle Tokyo. All sites have both marine and non-marine sediments up to 50–60 m in thickness. We determined trace element concentrations in the pore water, pH, EC, and loss on ignition. The results show that (1) the marine sediments tend to have low pH, high EC, and high sulfur concentration compared to the non-marine sediments (2) the concentration of most of the soluble heavy metals vary depending on the concentration of sulfate, the pH, and the formation processes of the strata, (3) the arsenic concentration is not related to sulfur concentration but apparently to Fe and Al concentrations, (4) the boron concentration is not related to any other properties implying that the boron level is independent of and cannot be predicted by common chemical properties, and (5) for all three sites, concentrations of most of the trace elements, EC, pH, and sulfate concentration were correlated with each other. This study shows that the concentration and potential mobilization of many toxic trace elements in marine sediments could be predicted by easily measurable pore water chemical properties such as pH and EC. This could be useful for predicting and avoiding the risk of groundwater pollution during underground development projects.  相似文献   

12.
Primary productivity of three size classes of phytoplankton (<5 μm, 5–22 μm, >22 μm) was measured monthly at six sites within San Francisco Bay throughout 1980. These sites in the three principal embayments were chosen to represent a range of environments, phytoplankton communities, and seasonal cycles in the estuary. Temporal variations in productivity for each size class generaly followed the seasonality of the corresponding fraction of phytoplankton biomass. The 5–22 μm size class accounted for 40 to 50% of the annual production in each embayment, but production by phytoplankton >22 μm ranged from 26% in the southern reach to 54% of total phytoplankton production in the landward embayment of the northern reach. A productivity index is derived that predicts daily productivity for each size class as a function of ambient irradiance and integrated chlorophylla in the photic zone. For the whole phytoplankton community and for each size class, this index was constant and estimated as ?0.76 g C m?2 (g chlorophylla Einstein)?1. The annual means of maximum carbon assimilation numbers were usually similar for the three size classes. Spatial and temporal variations in size-fractionated productivity are shown to be primarily due to differences in biomass rather than size-dependent carbon assimilation rates. *** DIRECT SUPPORT *** A01BY034 00005  相似文献   

13.
The benthic amphipod Ampelisca abdita dominates mudbottom benthic communities in Jamaica Bay (New York). In this study, we investigated the trophic role of Ampelisca in relation to winter flounder (Pleuronectes americanus) populations—the most frequently trawled fish species in Jamaica Bay. Flounders collected by trawl during summer 1989 were primarily juveniles. Stomach analyses indicated that amphipod crustaceans contributed >99% of prey individuals, with A. abdita making up 88%. Density and size frequency analyses of Ampelisca at three sites indicated two overlapping cohorts: a spring cohort released in June and a summer cohort released in late summer. Most overwintering survivors come from the summer cohort. Secondary production of Ampelisca was estimated at three sites using the cohort summation of biomass method. Estimates of annual production ranged from 25 g DW to 47 g DW m?2 (mortality + residual biomass); production due to growth ranged from 20 g DW to 26 g DW. Simulations of spring cohort production using a range of plausible growth and mortality schedules suggested that P∶B may be more sensitive to variability in survivorship than growth. Ampelisca secondary production in Jamaica Bay is compared with other amphipod species and with macrobenthic production in other coastal and estuarine systems. We conclude that observed amphipod production is probably more than sufficient to support local winter flounder populations in Jamaica Bay, and we speculate that high nutrient loadings may indirectly stimulate amphipod production. *** DIRECT SUPPORT *** A01BY058 00010  相似文献   

14.
The initial flooding waters from twenty-four consecutive tides were examined for changes in water properties as the flood-front traversed the intertidal zone. The flood-front water temperature depended on the time of flooding as well as the sun’s insolation. On warm sunny days, the water temperature at the leading edge of the tide successively increased as the water flooded the tidal flat. In contrast, during cloudy days, and early morning and evening samplings, the flood-front water decreased during flooding. Flood-front water temperatures on warm days exceeded 34°C, some 15°C higher than the water observed in the deeper tidal channels. Flood-front salinities increased progressively across the intertidal zone regardless of local weather conditions, and were primarily controlled by mixing of surface waters with interstitial waters during the flooding process. Particulate matter concentrations were dependent on the interaction between small amplitude waves and varying intertidal bottom slope. Extreme variability in the particulate matter concentration across the tidal flat was in part caused by alternate resuspension and settling of fecal pellets composed of silty-clay aggregates which partly form the bottom sediment of the test area. The texture of the suspended particulate matter coarsens near shore, where wave resuspension became more effective on a steeper portion of the intertidal zone. *** DIRECT SUPPORT *** A01BY009 00003  相似文献   

15.
Oxygen profiles were measured in the sediments of the Gulf of Aqaba (Red Sea), an oligotrophic marine system affected by episodic seasonal flash floods and intense aeolian dry deposition. Sediment cores were retrieved from shallow (15–45 m), intermediate (250–561 m) and deep (700 m) water sites of south–north and east–west transects. Dissolved oxygen concentrations were measured simultaneously by using microelectrodes and microoptodes immediately after sampling and after transportation. Oxygen penetration depths were found to increase from 2 to 5 mm at the shallow water sites with sandy permeable sediments to 10–21 mm at the deeper sites with cohesive muddy sediments. This increase corresponds to decrease in oxygen diffusive fluxes at the sediment–water interface and oxygen consumption rates with depth. Oxygen consumption rates exhibit local maxima at the oxic–anoxic sediment boundary, which may be attributed to oxygen reduction coupled to oxidation of dissolved Fe(II) and Mn(II) at deep and intermediate water sites and of hydrogen sulfide at shallow water sites. Microelectrodes and microoptodes measurements of cohesive sediments from deep and intermediate water sites yielded similar results. By comparison, the microoptodes displayed more robust measurements than microelectrodes in sandy near-shore sediments. This was attributed to their flexible fiber structure that is less likely to break or to abruptly displace sand particles. After transportation of sediment cores from Eilat to Beer Sheva followed by ≤?24-h storage, no changes in oxygen fluxes and consumption rates were detected.  相似文献   

16.
Geotechnical property analyses on sediments recovered by DSDP drilling within select convergent margins were integrated to determine the variability in these properties along the trench inner-slope and to delineate the effects of convergence on these properties. Consolidation states range from very underconsolidated to highly overconsolidated, with preconsolidation pressures exceeding 46,000 kPa in Quaternary sediments. Underconsolidated sediments are attributed to:
1. (1) high sedimentation rates.
2. (2) low sediment permeability relative to the length of the drainage path; (3) laterally applied stresses; and (4) induced pore water pressures resulting from the subduction of pelagic sediments with high water content. Factors contributing to the state of overconsolidation include: (1) tectonically induced overpressures; (2) removal of overburden by mass movement processes.
3. (3) low sediment accumulation rates.
4. (4) age.
Vertical gradients of index properties also vary greatly with the maximum gradient associated with overconsolidated sediments. Values of porosity generally exceed 30% at all margins studied, suggesting this porosity represents the minimum attainable solely by the effects of convergence.Geotechnical property results and site-specific parameters suggest two end members should be considered in the general geotechnical property model for convergent margin sediments. Clastic dominated margins form the basis for the initial geotechnical property model. These margins are characterized by thick trench sediment sequences which are folded and faulted and become progressively more deformed upslope. Convergence rates are low, and no well-developed faults or hrst and graben structures are evident on the downbending oceanic plate. Highly overconsolidated sediments and index property values which change rapidly with depth result from the slow progressive deformation of trench and lower slope sediments. Examples of clastic-dominated margins include the Nankai Trough, Aleutian Trench, and Washington continental margin.Pelagic-dominated margins have significantly different geotechnical properties and site-specific parameters. These margins are characterized by thin clastic trench sediment sequences overlying pelagic sediments on a rapidly converging oceanic plate. Well-developed faults and/or hrst and graben structures are evident on the downbending oceanic plate. Sediment deformation along the trench and lower slope appears limited. These sediments are underconsolidated and index property values change gradually but often irregularly with depth. Japan Trench and Middle America Trench-Guatemala margins are considered pelagic-dominated. Middle America Trench-Mexico appears to represent an intermediate case having characteristics of both margin types.  相似文献   

17.
The Houjing River flows through Kaohsiung, the most industrialized city in southern Taiwan. In this study, heavy metal concentrations in water and sediments from samples along the river were investigated to illustrate metal contamination levels and call for the awareness of industrial pollution prevention. The heavy metal concentrations in the water samples were low and appear to pose little direct risk to aquatic life and irrigation, but heavy metal concentrations in the sediments are locally very high and present an environmental risk. Cadmium, Cu, and Zn were found in higher concentrations in the river sediments than those recommended in some sediment quality guidelines and findings of river sediments in similar studies worldwide. Hence, the ecological risk of heavy metal contamination in sediments was assessed using the pollution load index (PLI) and potential ecological risk index (RI). Three of the eleven sites sampled were found to have PLI values higher than 1 and 8 of them had ‘considerable’ to ‘very high’ RI values, suggesting a considerable ecological risk. These findings provide an insight into elemental metal contamination of the Houjing River and present a baseline data set, which will be critical for future development and environmental protection plans devised for the region.  相似文献   

18.
Quantitative climate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Recent advances in molecular geochemistry have led to calibrations using glycerol dialkyl glycerol tetraethers (GDGTs), a group of temperature-sensitive membrane lipids found in Archaea and bacteria. GDGTs have been used to construct temperature indices for oceans (TEX86 index) and soils (MBT/CBT index). The aim of this study is to examine GDGT-temperature relationships and assess the potential of constructing a GDGT-based palaeo-thermometer for lakes. We examine GDGT-temperature relationships using core top sediments from 90 lakes across a north-south transect from the Scandinavian Arctic to Antarctica including sites from Finland, Sweden, Siberia, the UK, Austria, Turkey, Ethiopia, Uganda, Chile, South Georgia and the Antarctic Peninsula. We examine a suite of 15 GDGTs, including compounds used in the TEX86 and MBT/CBT indices and reflecting the broad range of GDGT inputs to small lake systems.GDGTs are present in varying proportions in all lakes examined. The TEX86 index is not applicable to our sites because of the large relative proportions of soil derived and methanogenic components. Similarly, the MBT/CBT index is also not applicable and predicts temperatures considerably lower than those measured. We examine relationships between individual GDGT compounds and temperature, pH, conductivity and water depth. Temperature accounts for a large and statistically independent fraction of variation in branched GDGT composition. We propose a GDGT-temperature regression model with high accuracy and precision (R2 = 0.88; RMSE = 2.0 °C; RMSEP = 2.1 °C) for use in lakes based on a subset of branched GDGT compounds and highlight the potential of this new method for reconstructing past temperatures using lake sediments.  相似文献   

19.
Stratification and bottom-water hypoxia in the Pamlico River estuary   总被引：1，自引：0，他引：1  
Relationships among bottom-water dissolved oxygen (DO), vertical stratification, and the factors responsible for stratification-destratification in this shallow, low tidal-energy estuary were studied using a 15-yr set of biweekly measurements, along with some recent continuous-monitoring data. Hypoxia develops only when there is both vertical water-column stratification and warm water temperature (>15°C). In July, 75% of the DO readings were <5 mg 1?1, and one-third were <1 mg 1?1. Severe hypoxia occurs more frequently in the upper half of the estuary than near the mouth. Both the time series data and correlation analysis results indicate that stratification events and DO levels are tightly coupled with variations in freshwater discharge and wind stress. Stratification can form or disappear in a matter of hours, and episodes lasting from one to several days seem to be common. Estimated summertime respiration rates in the water and sediments are sufficient to produce hypoxia if the water is mixed only every 6–12 d. There has been no trend toward lower bottom water DO in the Pamlico River Estuary over the past 15 yr. *** DIRECT SUPPORT *** A01BY059 00002  相似文献   

20.
《Applied Geochemistry》1997,12(5):593-605
The impact of sediment type on stream water geochemistry was studied in a catchment in Finland affected by sulphidic fine-grained sediments. Stream water samples for general characterisation of water quality (pH, electrical conductivity) were taken at the basin outlet during various hydrological conditions, while samples for detailed geochemical analysis were collected at 119 sites in the catchment on one single occasion during high-water flow in autumn. The occurrence of sulphidic fine sediments was estimated based on data from an airborne electromagnetic survey carried out by the Geological Survey of Finland.Growing-symbol maps, which were prepared for each of the studied variables in water, and statistical calculations including factor analysis and Spearman correlations show that the concentrations of Al, Ga, U and Tl, all the lanthanides and several alkali and alkaline earth metals (K, Mg, Na, Li, Ca, Rb, Sr), transition metals (Cd, Co, Cu, Zn, Sc, Mn, Ni, Y, Hf) and non-metals (S, Br, I, Si) increase in water when the proportion of the catchment cover of sulphidic fine sediments increases. It is therefore argued that these elements are released and mobilised in considerable amounts by the oxidation and subsequent acidification and weathering of this type of sediment. Other elements are either slightly depleted in streams in areas of sulphidic fine sediments (V, Nb, Pb, Zr), have a distribution unrelated to sediment type (Fe, Cr, Cs, Mo), or are only weakly impacted by the occurrence of sulphidic sediments in the catchment (As, Ti, Ba). It is argued that these elements are not leached extensively from the oxidising sulphidic sediments, and that their distributions at least partly may be controlled by the contents of dissolved humic material and/or suspended organic and inorganic phases in the water.  相似文献   

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